Mineral filled paper



MINERAL FILLED PAPER Tyrrell H. Werner, Westbrook, William H. Man-a, Portland, and Warren B. Gilman, Gorham, Maine, assignors to S. D. Warren Company, Boston, Mass., a corporation of Massachusetts No Drawing. Filed June 13, 1955, Ser. No. 515,238

9 Claims. (Cl. 162--178) This invention relates to a loading agent or filler adapted for use in making paper and other uses, to the method of making said filler, to the method of using said filler in making paper and to the paper product of said method.

This application is a continuation-in-part of our application Serial No. 449,261 tiled August 11, 1954, now abandoned.

Whenever paper is mentioned herein the name is intended to and does include all products made in whole or in part of cellulosic fiber felts deposited from Water or aqueous suspensions.

Briefly and in general terms the invention is based upon the discovery that improved results may be obtained by incorporating loading agents or fillers into paper together with an organic colloid material in such a way that the particles of filler are wholly or partly coated with the organic colloid material prior to or simultaneously with their deposition upon the cellulosic fibers of which the paper felt is formed.

By improved results we mean that the filler is retained in the paper web as well or better than when alum is used, the known harmful efiects of alum are avoided, and a stronger paper is produced.

It is well known to incorporate loading agents or fillers such as clay, calcium carbonate and other finely divided mineral materials into paper. Ordinarily this is done by adding the filler material to the aqueous suspension of the cellulose fibers before or after beating or other mechanical treatment of the fiber suspension in preparing it for the production of the paper web. The suspension subjected to this mechanical treatment generally contains from 95% to 97% by weight of water. It is customary after the mechanical treatment, that is, either before or after the addition of the tiller, to dilute the pulp to a water content of about 99% by weight before delivering it to the web forming means, e.g. the wire screen of a paper making machine. At the wire screen most of the water content of the pulp drains through the wire screen and carries a substantial part of the filler with it. This filler may be discarded with the water or it may be recovered, that is, returned to the process. Many expedients have been practiced for the purpose of preventing this loss of filler from the paper web, the most commonly used of which is the addition of paper-makers alum (aluminum sulfate) to the aqueous suspension of cellulosic fiber before or after the heating or other mechanical treatment. The dissolved alum or aluminum sulfate is acidic and generally renders the pulp acidic and aside from its ability to increase the retention of filler in the paper web its use generally is regarded as being detrimental. For instance it has a deleterious effect on the ageing properties of the paper and reduces the strength of the bond between the cellulosic fibers. Besides the water in which the cellulosic fibers are suspended frequently contains colored impurities which are coagulated and precipitated by the alum and are retained in the paper web whereas if alum were not used such colored impurities would pass on with the water. The use of alum is particularly objectionable when the filler is or contains calcium carbonate which reacts readily with the acid liberated by the alum.

The present invention obviates the use of alum and the objectionable features associated therewith. In accordance with the present invention the retention of the filler in the paper web is promoted by the organic colloid material associated with the filler.

In accordance with the present invention the filler particles may be precoated completely or partially, that is, the coating may be in the form of a complete envelope or in the formof one or more spots on thefiller particle.

The coating material is a swelled and water-dispersed organic colloid material which is derived fromplant seeds or corms. It is of the plant mucilage class which consists largely of one or more of the substituted mannans which are complex poly-saccharides. The plant mucilages either swell to a jelly in water to form mucilaginous semiliquids, or disperse in water to form colloidal systems, or dissolve in water. The substituted mannan plant mucilages are insoluble in ethyl alcohol. The entire class of plant mucilages is described in numerous text-books, such as in vol. 7 of the Encyclopedia of Chemical Technology, published in 1951 by Interscience Encyclopedia, Inc.

The term substituted mannans is used herein to designate the polygalactosylmannans and polyglucosylmannans which are commonly referred to respectively as galactomannans or mannogalactans and as glucomannans. The terms mannogalactan and galactomannan are used interchangeably hereinafter.

This invention uses those plant mucilages which swell and are colloidally dispersed in water at suitable temperature and which form coatings on the particles of mineral filler whereby the coated particles are attracted to and retained by the cellulose fibers. The coating composition need not be a pure substituted mannan and it may include water-soluble or dispersible starch and starch derivatives if enough substituted mannan is used in proportion to the total weight of the filler.

In order to pre-coat the particles of mineral filler, a swelled and colloidal dispersion of the coating composition can be made, and this can be mixed with the particles of mineral filler. a

As an alternative, the particles of mineral filler may be mixed with water, and the dry ingredient or ingredients of the coating material can be swelled and colloidally dispersed in the resulting mixture.

In either case, the particles of mineral filler do not form a stable suspension in the aqueous colloidal dispersion of the substituted mannan. The particles of mineral filler will separate from said aqueous colloidal suspension by sedimentation, if the entire mixture is allowed to. stand at 20 C.-30 C. The particles of mineral filler, can be kept in fine and uniform suspension however by gently agitating the final mixture. The colloidal dispersion of the substituted mannan does not act as a stabilizing or peptizing agent, unlike many gums which are used to produce stable suspensions. The particles of mineral filler can be separated from the aqueous colloidal dispersion by ordinary filtration. 7

The substituted mannans of the classes contemplated for use according to the invention may usually, it given enough time and agitation, swell and disperse in water at room temperature (20-25 C.) sufficiently to be effective. oftentimes, however, it is more convenient to effect the dispersion more quickly at a higher temperature, such as 6595 C. w

The swelled and colloidal dispersion of the coating material is made with a sufliciently high proportion thereof relative to the amount of water that the particles of mineral filler can adsorb or absorb or take up the swelled and colloid-ally dispersed coating material to form the desired coating of said swelled and colloidally dispersed organic colloid material, either on the entire surfaces of said particles, or on one or more spots of said particles. Said particles retain said coatings when said particles are mixed with the cellulose fibers while said cellulose fibers are in aqueous suspension and said particles retain said coatings in the initial paper web and in the finished a er. P coating on each particle causes the coated particle to be attracted to and to adhere to the cellulose fiber in the aqueous suspension so that a large proportion of the pre-coated filler is retained in the initial paper web and also in the finished paper.

It is known to use the plant mucilages of the mannogalactan class in making paper, as disclosed in the following United States Patents:

Number Date 2,644,751 July 7, 1953 2,644,752 July 7, 1953 2,644,763 July 7, 1953 However, the manno-galactans have not been used according to the patents, to pre-coa-t the particles of mineral filler and such pre-coating of said particles as later described herein is believed to be broadly novel. Said manno-galactans, in prior practice, have been added directly to the aqueous suspension of the cellulosic fibers, either before or after the addition of uncoated mineral filler to said aqueous suspension of the cellulosic fibers in order to strengthen the paper and for other purposes.

The aqueous suspension to which the manno-galactans have been added in prior practice, have had a very large proportion of water. The manno-galactans did not efficiently coat the particles of mineral filler to get the results later stated herein. The manno-galactans were primarily or largely attracted to the cellulose fibers, instead of coating the particles of mineral filler.

According to the present invention, the solid ingredients of the aqueous blend which is supplied to the wire screen of the Fourdrinier machine or other web-making machine, may consist only of cellulosic fiber which is intimately mixed with the pre-coated particles or mineral filler. Other solid ingredients are optional. The optional ingredients include rosin size, coloring matter and the like. Alum may be added, but one great advantage of the present invention is that alum is not necessary for efficient filler retention.

According to the preferred form of the invention, the cellulose fibers are beaten or otherwise mechanically worked while they are suspended in an aqueous liquid of substantial alkalinity, that is, at a pH value of 8.5 or higher, as up to a pH value of 12.5. This is rendered possible by the elimination of added alum and other added acid agents. If necessary, the pH value can be adjusted to said preferred minimum pH value of 8.5 or more, by dissolving an alkaline agent in the water of said aqueous suspension of the cellulose fibers, such as by dissolving therein sodium hydroxide, potassium hydroxide, pure sodium carbonate or commercial crude sodium carbonate or soda ash. Superior mechanically worked or beaten cellulose fiber is secured by mechanically working the cellulose fibers under such alkaline condition. After the mechanical working of the cellulose fibers has been completed, the pre-treated particles of the mineral filler are added to the aqueous suspension of the pre-beaten or pre-worked cellulose fibers. Moderate mixing then forms a uniform mixture of the cellulose fibers and the pretreated particles of mineral filler. The pre-coated particles of filler are attracted to the cellulosic fibers in the aqueous suspension.

In a less preferred form of the invention, the cellulose fiber is fully beaten or mechanically worked in aqueous suspension under less alkaline conditions or even under acidic condition, and the pre-treated fine particles of mineral filler are then mixed with the aqueous suspension of the pre-worked cellulose fibers, to be attracted to the fibers.

Some papers have little mineral filler and a large proportion of mechanical pulp. This mechanical pulp is made by grinding wood or other source of cellulosic material, without chemical cooking. These papers include printing papers. 'They require very little heating or other preparation for the purpose of making a web. The invention applies to such papers.

However, in most cases, the aqueous suspension of the cellulose fibers requires vigorous mechanical working of said fibers, whereby the cellulose fibers are pressed, torn and macerated, in order to swell and hydrate said cellulose fibers and to form the thin fibrils thereon. In such case, it is desirable to complete the mechanical working prior to adding the pro-treated or pre coated fine particles of mineral filler. Some of the pre-treated mineral filler will escape from the paper web, together with the drainage water from the paper web which flows through the openings of the wire screen of the web-forming machine. This escaping water can be collected and returned to another aqueous suspension of the cellulose fibers, so that there is very little loss of the pro-treated filler.

The pH of the aqueous suspension of the cellulose fibers is not a critical factor for the retention of the pre-coated mineral filler. There is good retention of the pre-treated filler in the paper web from aqueous suspensions of the cellulose fibers at pH values in which the use of aluminum sulfate has little beneficial efiect in retaining the uncoated 'cfiller. Good retention of pre-treated or pre-coated filler in the paper web is secured, even if the water of the aqueous suspension of the cellulose fibers which is used to make the paper web, has a pH as low as 3.0, or is in a pH range of 3.0 to 12.5. It is preferred to have a pH of at least 6.0, and even more preferably, a pH of 7.0 or higher.

By beating or mechanically working the cellulose fibers in an aqueous suspension under alkaline conditions, especially at a pH of 9.0 or higher, much more web-forming strength is developed, for the same expenditure of energy, than by heating or mechanically working under acid condition. Paper made from cellulose fiber which is beaten or otherwise mechanically worked under alkaline condition, is stronger than paper which is beaten or otherwise mechanically worked in the same manner for the same length of time under acid condition. Part of the beneficial effect of heating or other mechanical working is lost, if the aqueous suspension of the cellulose fibers is made acid at any time before forming the paper Web or at the time of forming the paper web. Hence, it is preferred to avoid the use of aluminum sulfate or other acid agent which lowers the pH value of the web-forming suspension of the fibers below the neutral point, which corresponds to a pH value of 7.0.

The invention can be used in making paper which has from 2% to 50% of mineral filler by weight, calculated on the air-dry weight of the air-dried and finished paper, which usually contains about 5% to 7% of water. This air-dry weight is designated as the dry weight of the finished paper. The invention is most useful in making paper which has 5% to 40% of mineral filler by weight, as calculated on said dry weight. This proportion of the filler is calculated on the airdry weight of the filler and of the paper and on the total weight of the air-dry paper. Thus, if the paper has 5% or five parts by weight of filler, said paper has or 95 parts by weight of cellulose fiber. As above noted, the pre-treated filler is optionally and preferably added after the mechanical working of the cellulose fibers has been fully completed. During the time that the cellulose fibers are being mechanically worked, the only filler which may be present in the aqueous suspension, is the runcoated filler which is present in paper scrap which may be one of the sources of the cellulose fibers, or coated filler in reused water which has drained from the paper web in a previous webforming operation according to this invention.

Without limitation thereto, the fillers are exemplified by clay, calcium carbonate, magnesium carbonate, talc, titanium dioxide, other suitable mineral pigments and mixtures thereof.

Calcium carbonate is the highly preferred filler, and the invention is particularly valuable in making it possible to use calcium carbonate efficiently.

The particle size of the filler which is coated or treated as described herein, may be in the range of onetenth micron (0.0001 millimeter) to 40 microns (0.040 millimeter). The preferred size range of the uncoated particles of filler is two-tenths micron to ten microns. The uncoated filler may be a mixture of particles of different sizes. One of the great advantages of the present invention is the efficient retention of fine filler particles, whose size is 0.5 micron or less.

The most common manno-galactans are present in or are derived from or are modified products of the gums of the following:

(a) Locust bean gum, also designated as carob bean gum or carob gum. 'Ihe botanical name of its source is Ceratonia siliqua L.

it has about 83% by weight of manno-galactans. It has been used in the paper industry for various purposes, such as, as a size and binder and finishing agent. It has never to our knowledge been used for the purposes of this invention.

This product is sold under the commercial name of locust bean gum and Lycoid gums. It is a substantially anhydrous powder.

As above noted, the invention is not limited to a pure manno-galactan. The coating medium can be a mixture of manno-galactan plant mucilage and a cationic water-soluble starch. 'Ilhis cationic starch is positively charged in aqueous solution.

(b) Guar gum. This is derived from a legume whose botanical name is Cyamposis psoralioides or Cyamposis tetragonaloba (psoralioides). It is sold commercially as guar gum or as Burtonite No. 7, in the form of a substantially anhydrous powder.

Other plant mucilages which have little commercial importance at a present time and which have at least 50% by weight of one or more manno-gal-actans, and which can be used herein, are found in or are derived from the seeds of the following sources:

(0) Flame tree: This is a class which includes the following: Nmysia floribzmda, family Loranthaceae. Brachychiton aerifolius, family Sterculiaceae. The Indian rhododendrum, whose botanical name is R. aboreum.

(d) The huisache shrub, whose botanical name is Vachellia farnesiana.

(e) The Kentucky coffee tree, whose botanical name is Gymn0cladus dioica.

(f) The mesquite, whose botanical name is Proscopz's juliflora.

(g) Palo Verde, whose botanical names are: Torreyanum, Cercidium torreyanum and Cercidium floridum.

The most common glucomannans are present in or derived from the following:

(a) Corms of the aroid commonly called konjak. The botanical name of its source is Amorphophallus konjak (rivereri) or Amorphophallus rivereri. The flour made from the corms is called konjak flour and it contains a high proportion of the glucomannan referred to as konjak mannan.

g i (b). Corms of the related aroid whose botanical name is Amo rphophallus oncopihyllus.

Whenever a unit is mentioned herein, this refers .to any unit of weight, such as a kilogram, pound, or 'pther unit of weight. Thus, as one example, one unit of said locust bean gum is mixedwith 100 units of water, and the mixture is heated to 91 C.,'with stirring, and the mixture is then additionally heated at 91 C., with stirring, for five minutes, and it may optionally then be cooled to 20 C.-30 C. All the operations described herein are carried out under ordinary atmospheric pressure and the heating and mixing operations described herein are performed with little or no loss of water. All measurements of pH and viscosity are made at 25 C. unless otherwise stated.

The resultant product has a pH of 6.0 and a viscosity of 2960 ce-ntipoises.

If the ratio of said locust bean gum is increased to 1.5 units, the resultant colloidal dispersion has a pH of 6.0 and a viscosity of 17600 centipoises.

The invention is not limited to 'a pH of 6.0 or above, in the colloidal dispersion.

Thus, as later described, we can use a colloidal dispersion of a product which is known commercially as Star gum No. 709. This product is a mixture of locust bean gum and starch which is water-soluble or water-dispersible. When one unit of said Star gum is colloidally dispersed in units of water, the resultant dispersion has a pH of 9.0, and a viscosity of 1600 centipoises. It is sufficient if the coated particles are electrostatically attracted to the cellulose fibers in the aqueous suspension thereof.

Cellulose fibers are negatively charged in aqueous suspension. Mineral fillers are also negatively charged in aqueous suspension. The pre-coating of the particles of mineral filler with the organic colloid material apparently positively charges the pre-coated particles of mineral filler in aqueous suspension, or at least lowers the negative charges of the uncoated particles, so that the pre-coated particles are attracted to the cellulose fibers in aqueous suspension and are then retained by the cellulose fibers.

As above noted, in order to be effective for purposes of filler retention, the swelled and colloidally dispersed coating material must have a sufficient concentration of the organic colloidal material relative to water, so that the colloidal material can coat the particles of mineral filler. If the mineral filler is thus intimately contacted with a sufiiciently concentrated swelled and colloidally dispersed coating ingredient or ingredients, the weight of the coating ingredient or ingredients may be a small percentage of the weight of the uncoated mineral filler. if the ingredient is a swelled and colloidally dispersed substituted mannan, and the coating composition has a sufiiciently high concentration of such substituted mannan relative to water, there is a marked improvement in filler retention if the air-dry weight of such swelled and colloidally dispersed substituted mannan in the mixture of water and colloid and mineral filler, is as low as one unit of said substituted mannan per 2,000 units of uncoated filler particles. Another important factor, which may even be the controlling factor, is that the mixture should be free from cellulose fiber, which attracts the substituted mannan, so that the substituted mannan coats the mineral filler.

For the purpose of retaining the pre-treated or precoated mineral filler in the initial paper web and in the finished paper, the preferred ratio in such mixture is from one unit to 100 units of substituted mannan, per 2,000 units of mineral filler, as calculated upon the air-dry weight of such substituted mannan and filler.

In most cases, as little as 10 units of substituted mannan is adequate, per 2,000 units of mineral filler. As above noted, the weight of the substituted mannan is calculated upon its air-dry weight or substantially its air-dry weight and the weight of the filler is calculated on its air-dry weight. The ratio of substituted mannan to filler depends to some extent upon the character of the cellulose material and the degree of beating thereof, which are factors in the retention of the tiller. However, on an average, the air-dry weight of the substituted mannan may be one-half percent of the air dry weight of the mineral filler.

If more of the substituted mannan is added beyond the amount which is required for good retention of the filler, the effect of the excess substituted mannan is chiefly to increase the strength of the finished paper. As above noted, it is old and well known to use manno-galactan for increasing the strength of the finished paper, especially when the finished paper is wetted with Water. The above ratios are calculated upon the use of locust bean gum, or manno-galactan, as the substituted mannan.

Example N0. 1

The manno-galactan used was locust bean gum. It was a substantially anhydrous powder.

One unit of this powder was mixed thoroughly with 100 units of water at C.-30 C. This water, as in the other examples, was ordinary tap water which was substantially neutral. The mixture was slowly heated up to 90 C. with constant stirring, and it was kept at 90 C. for five minutes with constant stirring. When optionally cooled to 20 C.-30 C., it was a stable and swelled colloidal dispersion of the plant mucilage in the water. There was little or no loss of water. This procedure was followed in making the aqueous swelled and colloidal dispersions of the starting material in the other examples, save for a difference in the maximum temperature.

This colloidal dispersion had the following properties:

pH 6.0. Viscosity 2960 centipoises.

As above noted, the pH and viscosity were determined at C.

A uniform aqueous suspension of titanium dioxide filler was made at 20 C. C., with 100 units of titanium dioxide and 400 units of water. This water, as in-the other examples, may be pure distilled water, or substantially neutral and pure water. This example shows one unit of locust bean gum per 100 units of filler, or a ratio of one percent by weight.

The colloidal dispersion of the locust bean gum was mixed with the aqueous suspension of the titanium dioxide, while said colloidal dispersion of the locust bean gum and said suspension were at 90 C. and 20 C. respectively. Any suitable mixing apparatus may be used for this purpose, such as a propeller stirrer. The mixing period may be only five minutes or the mixing period may be several hours until the mixture is ready for use. The mixture may be allowed to stand and then stirred when ready for use.

Cotton rags were cooked in an alkaline liquid, in order to make a chemical cellulose pulp. The usual operations subsequent to cooking and prior to forming the aqueous suspension of the cellulose pulp for beating, are not described, because they are well known and do not form part of the invention.

The aqueous suspension of the chemical pulp which was beaten, was 5% by weight and contained about 1500 pounds of pulp, air-dry.

The pH of the water of said aqueous suspension was 7.0 to 9.0.

The chemical pulp was beaten at said pH of 7.0 to 9.0.

The mixture of filler, water and dispersed locust bean gum was mixed with the aqueous suspension of the cellulose fibers after full prior beating and refining and with minimum further working of the cellulose fibers, as by -flowing the aqueous suspension and said mixture through a common pump, or by ordinary gentle agitation so that the pre-coated filler is attracted to and fluocculated with the cellulose fiber. The visible effect is that the pre- 8 coated particles migrate from the water to the cellulose fibers.

The blend was made into a paper web which was finished according to standard procedure. This paper had no sizing and consisted substantially only of cellulose fiber and the filler and the locust bean gum.

The finished paper sheet was of exceptional whiteness and it had 5.5% by weight of the titanium dioxide filler and 94.5% of cellulose fiber, calculated on the air-dry weights.

Hence a small part of the titanium dioxide escaped with the drainage water through the openings of the wire screen of the web-forming Fourdrinier machine.

After the mixture of the filler with the colloidal dispersion of the manno-galactan or mixture of which a manno-galactan is a part has been made, and the filler has been coated by thorough mixing, the coated particles of filler can be separated by filtration for addition to an aqueous suspension of cellulose fibers.

Also the mixture may be made with a high solids mixer of the kneading type, so that the mixture is a paste which contains up to 70% by weight of the filler, with a small percentage of gum, and such paste mixture can be conveniently stored and shipped.

While it is highly preferred to add the pre-coated filler to an aqueous suspension of the cellulose fiber or pulp after full beating or other mechanical working of the fiber, it is within the scope of our invention to add the pre-coated filler to the pulp before it is beaten or after it is only partly beaten and then to carry out or complete the mechanical treatment of the fiber.

Example N 0. 2

The cellulose material was a bleached chemical pulp of long and short wood fibers, which had been cooked by the soda process.

The aqueous suspension was beaten moderately, according to usual practice, while the pH of its water was about 7.0.

The aqueous suspension had 5% of cellulose fibers by weight, calculated on their air-dry weight.

This aqueous suspension of the beaten pulp was given a slight blue color by adding a phosphotungstic lake of Victoria Blue. Aluminum sulfate was then dissolved in the water of said suspension, in sutficient amount to lower its pH to 6.0, in order to set the coloring matter.

A colloidal dispersion of the locust bean gum was prepared as previously described, using one unit of said gum and units of water.

An aqueous suspension of filler clay was made in water, using 66 units of clay and 264 units of water.

The colloidal dispersion and said clay suspension were mixed as above described, to form a final mixture, in which there were three units of the plant gum to 200 units of the clay, calculated on their air-dry weights.

This final mixture was added to the aqueous suspension of the pro-beaten fibers, using the above-mentioned procedure with moderate mixing.

The resultant aqueous blend had about 17 units of clay per 100 units of cellulose fiber, calculated on their airdry weights.

The resultant air-dry paper sheet which was formed from this blend had 11% by weight of the clay filler and 89% by weight of cellulose fiber, corresponding to about 12 units of clay filler to 100 units of cellulose fiber, so that about 30% of the filler in the aqueous blend escaped from the paper web, but was recovered for reuse by well known procedure.

Example No. 3

The plant mucilage was guar gum. It was a substantially anhydrous powder.

One air-dry unit of said guar gum was swelled and dispersed in 100 units of water, using the above procedure. This dispersion had a pH of 6.2 and a viscosity of 3800 centipoises.

50 units of finely divided commercial precipitated calcium carbonate were suspended in 200 units of water. The weight of the gum was 2% of the Weight of the calcium carbonate, calculated on their air-dry weight.

The guar gum dispersion was stirred into said suspension of the calcium carbonate, using the above procedure, to make a final mixture.

The concentration of the colloidally dispersed guar gum in this final mixture was sulficient to cause it to be adsorbed by the fine particles of calcium carbonate, which formed a fine and uniform but not stable suspension in the final mixture, as in the other example.

The aqueous suspension of the cooked and beaten cellulose fibers were free from alum. It had a pH of 9.

The aqueous suspension of the cellulose fibers had by weight of cellulose fibers, calculated on the air-dry weight of said cellulose fibers. The air-dry weight of the fibers was 125 units.

Hence the blend which was used to make the paper web had 50 units of calcium carbonate to 125 units of fiber.

The finished paper web, in air-dry weight, had 20 units of calcium carbonate filler to 80 units of cellulose fiber.

Hence, in the aqueous blend, the weight of the calcium carbonate was 40% of the weight of the fiber, calculated on their air-dry weights.

In the finished paper, the weight of the filler was 25% of the weight of the fiber.

About 15% of the filler, based upon the air-dry weight of the fibers, escaped through the wire screen with the drainage water, which could be recovered for re-use by the procedure commonly used to recover such filler.

This retention of the calcium carbonate, without the use of alum, in large scale commercial practice, is an exceptional result.

Example No. 4

One unit of said locust bean gum was swelled and colloidally dispersed in 100 units of water as above described.

200 units of finely divided calcium carbonate were suspended in 800 units of water.

The final mixture was made as above described.

The cooked cellulose fibers were of ordinary commercial type and they were beaten in an aqueous suspension which had a pH of 9.0. This suspension had 666 units .of cellulose fiber (air-dry weight) in a 5% aqueous sus- Example N0. 5

Wood chips were cooked by the soda process to produce chemical pulp. After usual preliminary operations, the resultant chemical pulp was suspended in water. This suspension had 5% by weight of cellulose fiber, calculated on the air-dry weight thereof. Crude commercial sodium carbonate was dissolved in the water of said suspension to provide a pH of 9.0.

This suspension was beaten moderately at said pH of 9.0 in a Hollander beater, and it was then refined at said pH of 9.0 in a Jordan engine, in order to provide uniform beaten cellulose fibers.

Five units of Star gum No. 709 were cooked in 300 units of water at about 88 C. for five minutes, with stirring, to provide a colloidal aqueous dispersion of said Star gum No. 709. This Star gum No. 709 is a 10 mixture of two parts by weight of locust bean gum and three parts by weight of watersoluble or water-dispersibl'e starch of the cationic type, which is attracted towards cellulose fibers which are negatively charged in aqueous suspension.

This colloidal dispersion of said Star gum had a pH of 9.0 and a viscosity of 1400 centipoises at 70 C.

250 units of clay were suspended in 1000 units of water. The colloidal dispersion of the Star gum was mixed with said aqueous suspension of clay to make a final mixture.

The air-dry weight of the locust bean gum was 0.8% of the air-dry weight of the clay filler.

This final mixture was mixed gently with the aqueous suspension of the cooked beaten and refined cellulose pulp and the mixture was formed into a finished air-dry paper which had 10 parts by weight of filler and parts of cellulose fiber.

Less than 40% of the filler which was added to the aqueous suspension escapeed through the wire screen of the web-making machine with the drainage water. This drainage water and the coated filler therein was used to dilute a fresh batch of the aqueous blend before it flowed to the wire screen, so that the overall recovery of the precoated filler was close to The maximum ratio of the filler to the fiber in the aqueous blend, calculated on airadry weights, never reached 20%.

The paper web was dried and machine-calendered. The paper web was considerably stronger than a comparable web made from an acidic suspension, and the color of the paper was excellent.

Example N0. 6

One unit of air-dry edible konjak flour containing at least 0.4 unit of glycomannan was suspended in 200 units of water and the suspension was then heated, with stirring, to 90 C. and held at 90 C. for 5 minutes to produce a viscous, substantially transparent dispersion of swollen konjak flour. The dispersion was then cooled to room temperature.

100 units of rfinely divided precipitated calcium carbonate were suspended in 367 units of water, and the suspension was mixed with the dispersion of swollen konjak flour whereby the particles of calcium carbonate became coated with said swollen konjak flour.

186 units of bleached fiber produced by pulping hardwood by the soda pulping process andlOO parts of bleached fiber made by pulping softwood by the sulfate pulping process were suspended in 7150 units of water containing sufficient dissolved sodium carbonate to keep the pH value of the suspension at about 9.0, and the suspended fibers were subjected to a moderate degree of beating in conventional beating and refining apparatus.

The suspension of beaten fiber was mixed with the suspension of konjak flour-treated calcium carbonate and with 45000 units of additional water to form a dilute mixture having fiber and filler in the ratio of 100 to 35. This dilute mixture was run out upon a paper-making screen to form a paper web which when dried had an air-dry weight of about 96 grams per square meter. This web contained over 30 grams of calcium carbonate to each 100 grams of air-dry fiber and was very white.

When aluminum sulfate is dissolved in water, the aluminum sulfate is partly hydrolyzed to produce flocculated and precipitated aluminum hydrate. The improved paper is free from precipitated aluminum compounds, such as aluminum hydrate, if made according to the preferred embodiment.

The minimum weight of the substituted mannan material, either as the sole ingredient or as one of the ingredients of the coating on the particles of mineral filler, is preferably one-quarter of one percent of the weight of the loading agent or filler. This is a good ratio. Said radio is calculated on the air-dry weights of the substi 11 tutedmannan material and the filler. Locus bean gum and-guar gum are the highly preferred galactomannan materials, and konjakmannan is the highly preferred glucomannan material.

As a result of the heat-drying of the initial paper web, the original coatings of the particles of loading agent are substantially dry.

If the filler is calcium carbonate alone, the minimum air-dry weight of the calcium carbonate is 2 to 3% of the air-dry weight of the entire finished sheet.

As stated above, the filler may be coated in several ways e.g. by adding a swelled colloidal dispersion of the coating material in Water to the dry filler or to an aqueous suspension of the filler or by adding the dry coating material to an aqueous suspension of the filler. In either case, the resulting suspension of coated filler constitutes a novel product adapted for use by addition to or incorporation in an aqueous suspension of cellulose fibers. It is further stated that a more highly concentrated coated filler, better adapted for sale or storage may be made by concentrating the coated suspension, however made, in any manner e.g. by filtration or evaporation of its water content to any degree including dryness and in any manner such as by spray drying which will leave the coated filler in a redispersible condition. Also as disclosed above concentrated coated filler composition may be made by kneading a mixture of filler, coating composition and Water with only sufficient water to form a paste. In carrying out this procedure the pigment, water, and coating composition may be added to the kneading machine in any order or any two of them or all three may be mixed together before introduction into the kneading machine. All such dispersed or dispersible coated pigment products are within the scope of our invention.

We claim:

1. In a method of making mineral-filled paper the steps which consist in coating finely divided mineral filler particles with an aqueous colloidal dispersion of plant mucilage in the form of a substituted mannan selected from the group consisting of manno-galactans and glucomannans by mixing an aqueous coloidal dispersion of the substituted mannan and the mineral filler particles, forming an aqueous pulp suspension containing cellulose fibers, intimately mixing the coated finely divided mineral filler particles with the said aqueous pulp suspension of cellulose fibers whereby the said coated finely divided mineral filler particles are attracted to the cellulose fi-bers and are retained in the said pulp in the absence of alum and its decomposition products and forming the pulp and included mineral filler into a paper web on a paper web-forming wire While draining surplus water therefrom.

2. The method defined in claim 1 in which the minimum weight of the substituted mannan in the coating on said finely divided mineral filler particles is one-quarter eral filler particles based on the air-dry weights of said substituted mannan and of said finely divided mineral filler particles.

3. The method defined in claim 1 in which the plant mucilage is a manno-galactan and in which the said aqueous colloidal dispersion contains cationic and waterdispersed starch.

4. The method defined in claim 1 in which the plant mucilage is a manno-galactan derived from the group of vegetable materials consisting of locust bean gum, guar gum, and the mucilaginous extracts of the seeds of the flame tree, the huirsache shrub, the Kentucky cofiee tree, mesquite, and palo Verde.

5. The method defined in claim 1 in which the plant mucilage is a glucomannan derived from a corm of an aroid selected from the group consisting of amorphophallus konjak and amorphophallus oncophyllus.

6. The method defined in claim 1 in which the finely divided mineral filler is calcium carbonate.

7. The method defined in claim 1 in which the pH of the mixture of coated finely divided mineral-filler particles and cellulose fiber pulp is in the range of 8.5 to 12.5.

8. The method defined in claim 1 in which the mixture of aqueous dispersion of plant mucilage and finely divided mineral filler is substantially free from cellulose fibers prior to being mixed with the cellulose fibers in the pulp.

9. Mineral filled paper consisting essentially of cellulose fibers and a finely divided mineral filler, the particles of said mineral filler having a coating thereon consisting of a plant mucilage of the group consisting of mannogalac tans and glucomannans, said paper having been made by the method defined in claim 1.

References Cited in the file of this patent UNITED STATES PATENTS 566,497 Castle Aug. 25, 1896 1,448,847 Kaiser Mar. 20, 1923 1,839,346 Seferiadis Jan. 5, 1932 2,287,153 Wallace June 23, 1942 2,322,185 Bicknell June 15, 1943 2,325,051 Gross July 27, 1943 2,644,749 Frisch July 7, 1953 2,644,763 Frisch et al. July 7, 1953 2,698,793 Landes Ian. 4, 1955 FOREIGN PATENTS 682,664 Great Britain Nov. 12, 1952 OTHER REFERENCES Erspamer: Paper Trade Journal, June 13, 1940, pages 3338, Tappi section, pages 321-326, 1940 ed. 

1. IN A METHOD OF MAKING MINERAL-FILLED PAPER THE STEPS WHICH CONSIST IN COATING FINELY DIVIDED MINERAL FILLER PARTICLES WITH AN AQUEOUS COLLOIDAL DISPERSION OF PLANT MUCILAGE IN THE FORM OF A SUBSTITUTED MANNAN SELECTED FROM THE GROUP CONSISTING OF MANNO-GALACTANS AND GULCOMANNANS BY MIXING AN AQUEOUS COLOIDAL DISPERSION OF THE SUBSTITUTED MANNAN AND THE MINERAL FILLER PARTICLES, FORMING AN AQUEOUS PULP SUSPENSION CONTAINING CELLULOSE FIBERS, INTIMATELY MIXING THE COATED FINELY DIVIDED MINERAL FILLER PARTICLES WITH THE SAID AQUEOUS PULP SUSPENSION OF CELLULOSE FIBERS WHEREBY THE SAID COATED FINELY DIVIDED MINERAL FILLER PARTICLES ARE ATTRACTED TO THE CELLULOSE FIBERS AND ARE RETAINED IN THE SAID PULP IN THE ABSENCE OF ALUM AND ITS DECOMPOSITION PRODUCTS AND FORMING THE PULP AND INCLUDED MINERAL FILLER INTO A PAPER WEB ON A PAPER WEB-FORMING WIRE WHILE DRAINING SURPLUS WATER THEREFROM. 